An experimental Chinese mRNA Covid-19 vaccine has been approved for late-stage clinical trials in Mexico after months of delay, as well as in Indonesia. The ARCoV vaccine – developed by Yunnan Walvax Biotechnology, Suzhou Abogen Biosciences and the Academy of Military Science – was cleared for the phase 3 trials by drug regulators in Mexico on August 19 and in Indonesia on August 27, Walvax said on Tuesday. The Mexico trial involving 6,000 people had been due to start at the end of May , the country’s foreign ministry said that month, but authorities postponed it without saying why. The Mexican health and foreign ministries did not respond to requests for comment. In its statement to investors on Tuesday, Shenzhen-listed Walvax said: “After the vaccine enters phase 3 trials, the company will increase investment in research and development.” The announcement came days after the vaccine maker got approval from the Nepalese government to conduct phase 3 trials on 3,000 people there, according to a report by Chinese state news agency Xinhua on Friday, citing a Nepali health official. Trials are also being conducted in China – in Yunnan province and in the Guangxi Zhuang region – although Covid-19 is no longer prevalent in the country. The phase 3 trials will test efficacy, safety and the immune response triggered by the vaccine in people aged 18 and over. Early registration records with online database ClinicalTrials.gov show some 28,000 people will take part in the trials worldwide, with at least 25 per cent of them aged over 60. They will be randomly assigned to study and control groups and given two doses of either the experimental vaccine or a placebo within an interval of 28 days. Walvax started building a facility in southwest China in December to produce its potential mRNA vaccine. The plant in Yuxi, Yunnan will have an initial annual capacity to make 120 million doses. Equipment is being installed and adjusted and it has gone through the required environmental protection assessment and awaits formal approval, according to Walvax’s semi-annual report released last week. ARCoV works by delivering engineered messenger RNA, or ribonucleic acid, that instructs human cells to produce proteins, which trains the immune system to respond in the presence of a real virus. China has relied mostly on inactivated vaccines for its mass vaccination drive against Covid-19, but studies have shown them to be less effective than the mRNA vaccines and authorities have encouraged drug makers to develop new vaccines using other technologies. Last month, Suzhou Abogen Biosciences, one of the developers of ARCoV, said it had raised over US$700 million to support the clinical development of its experimental vaccine and to expand the pipeline of other vaccine and treatment candidates. Several other Chinese drug makers are also experimenting with other technologies, including mRNA, protein-based and adenovirus-vectored vaccines. In June, Stemirna Therapeutics in Shanghai raised US$200 million for its Covid-19 vaccine candidate that uses mRNA technology and is going through phase 2 human trials. It is also testing the candidate on people who have already been inoculated with inactivated vaccines, according to record site Chinese Clinical Trial Registry.